Apparatus for locating the position of a spinal implant during surgery

ABSTRACT

An apparatus and method for locating the position of a spinal implant in an intradiscal space patient during surgery, comprising a spinal implant formed of radiolucent material and a releasably attached inserter comprising a positioning element including thereon a marker of material more radiopaque than the material of the spinal implant. The positioning element extends into the implant such that the marker is positioned at a predetermined location within the implant, the positioning element with the radiopaque maker being removable from the spinal implant after insertion. In a particular method of locating the position of the spinal implant, the spinal implant is inserted from the lateral approach.

FIELD OF THE INVENTION

The subject invention relates generally to the field of spinal implantsand more particularly to instruments and methods for locating withimaging techniques the position of such implants during insertion into apatient.

BACKGROUND OF THE INVENTION

Implants such as spinal interbody fusion devices are used to treatdegenerative disc disease and other damages or defects in the spinaldisc between adjacent vertebrae. The disc may be herniated or sufferingfrom a variety of degenerative conditions, such that the anatomicalfunction of the spinal disc is disrupted. Most prevalent surgicaltreatment for these conditions is to fuse the two vertebrae surroundingthe affected disc. In most cases, the entire disc will be removed,except for a portion of the annulus, by way of a discectomy procedure. Aspinal fusion device is then introduced into the intradiscal space andsuitable bone or bone substitute material is placed substantially inand/or adjacent the device in order to promote fusion between twoadjacent vertebrae.

Spinal fusion devices may be inserted during a spinal surgical procedureusing an anterior, posterior, posterior lateral, lateral orextrapedicular approach. Examples of expandable spinal interbody fusiondevices are described in U.S. Pat. No. 6,595,998 entitled “TissueDistraction Device”, which issued on Jul. 22, 2003 (the '998 Patent) andU.S. Pat. No. 7,967,867 entitled “Expandable Interbody Fusion Device”,which issued on Jun. 28, 2011 (the '867 Patent). Spinal fusion devicesmay also be non-expandable, monolithic devices of fixed dimension, asshown for example, in U.S. Pat. No. 7,749,269 which issued on Jul. 6,2010 and is assigned on its face to Warsaw Orthopedic, Inc. (the '269Patent) and U.S. Pat. No. 7,918,891 which issued Apr. 5, 2011 and isassigned on its face to NuVasive Inc. (the '891 Patent). The spinalfusion devices described in the '269 Patent and the '891 patent areparticularly configured for insertion into the intradiscal disc spacefrom the lateral approach, with such implants having a length that whenpositioned in the disc space from one lateral side to the other theimplant may rest on the cortical rims of both opposing lateral sides ofa vertebral body.

One of the issues facing a surgeon during spinal surgery is the properpositioning of the implant in the intradiscal disc space. Spinal fusionimplants are frequently made of materials such as polyetheretherketonepolymer (PEEK) for strength and other biocompatible properties. However,since such materials are often radiolucent they are difficult tovisualize under X-rays or fluoroscopy. To enable visualization, aradiopaque material such as a metal marker or barium sulfate may becombined with the implant material when the implants are manufactured,such as described in the '998 Patent. Visualization elements may also beprovided in the form of spike elements or pins located at the proximaland distal ends of the implant as well as in a medial support betweenfusion apertures, as shown, for example, in the '891 Patent.

While such known visualization have been generally satisfactory, therenevertheless remains a need for improvements in surgical techniques toassist the surgeon in determining the proper position of a spinalimplant during the implantation procedure.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an apparatus and method forlocating the position of a spinal implant in an intradiscal spacepatient during surgery, comprising a spinal implant formed ofradiolucent material and a releasably attached inserter comprising apositioning element including thereon a marker of material moreradiopaque than the material of the spinal implant, the positioningelement extending into the implant such that the marker is positioned ata predetermined location within the implant, the positioning elementwith the radiopaque maker being removable from the spinal implant afterinsertion. In a particular method of locating the position of the spinalimplant, the spinal implant is inserted from the lateral approach.

It is a further object of the invention to provide a kit of partscomprising an inserter, a plurality of spinal implants each of which hasa different maximum length, and a plurality of positioning elements eachof which is adapted to be individually supported by the inserter forextending into a correlated implant, each of the plurality ofpositioning elements having a radiopaque marker thereon at a differentlocation.

DESCRIPTION OF THE FIGURES

FIG. 1 is an exploded perspective view of an apparatus according to anembodiment of the subject invention for locating the position of thespinal implant during surgery showing the spinal implant and componentsof the implant inserter.

FIG. 2 is a top perspective view of the spinal implant of FIG. 1.

FIG. 3 is a top plan view of the spinal implant of FIG. 2

FIG. 4 is a side elevation view of the spinal implant of FIG. 2.

FIG. 5 is a longitudinal cross-sectional view of the end of theassembled inserter of FIG. 1 attached to the spinal implant.

FIG. 6 is a side elevation view of the distal end of the inserterattached to the spinal implant similar to that of FIG. 6 showing theenhanced visualization characteristics of an embodiment of the subjectinvention under fluoroscopy.

FIG. 7 is a side elevation view similar to that of FIG. 6 showing theintroduction of a spinal implant into the intradiscal space of a spinefrom the lateral approach under fluoroscopy.

FIG. 8 is a top perspective view of an alternative arrangement thespinal implant of FIG. 2.

FIG. 9 is an perspective view of an alternative arrangement wherein apositioning element useful in the apparatus of FIG. 1 is formed as aseparate piece suitably attachable to the distal end of elongate rod ofthe apparatus.

DESCRIPTION OF THE EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the drawing figures and thefollowing written description. It is understood that no limitation tothe scope of the invention is thereby intend. It is further understoodthat the present invention includes any alterations and modifications tothe illustrated arrangements and further includes applications ofprinciples of the invention as would normally occur one skilled in theart to which this invention pertains.

Referring now to FIGS. 1-4, there is shown an apparatus 10 that includesa spinal implant 12 and an inserter 14 for locating the position ofspinal fusion implant 12 in a patient during surgery. In this particulararrangement, spinal implant 12 has a bi-convex configuration for use ininterbody spinal fusion and is introduced into the intradiscal spacebetween two opposing vertebral bodies of a patient from the lateralapproach. It should be appreciated however, that spinal implant 12 mayalso be configured for other applications and may be inserted during aspinal surgical procedure using an anterior, posterior, posteriorlateral, or extrapedicular approach. Inserter 14 includes an elongateconnection rod 16 for releasably connecting inserter 14 to spinalimplant 12 and for assisting in locating the position of spinal implant12 in the intradiscal space, as will be further described.

Turning now to FIGS. 2-4, details of spinal implant 12 are set forth.Spinal implant 12 is generally of parallelepiped configurationcomprising a distal front wall 18, a spaced opposed proximal rear wall20 and a pair of spaced opposed sidewalls 22 and 24 extending betweenfront wall 18 and rear wall 20. In this arrangement, front wall 18 andrear wall 20 and generally parallel to each other with sidewalls 22 and24 being generally parallel to each other. Front wall 18 includes adistal leading surface 18 a and rear wall 20 includes a proximaltrailing surface 20 a. Implant 12 includes a top surface 26 and a bottomsurface 28 each of which may be formed in a preferred arrangement tohave a convex configuration between front wall 18 and rear wall 20 aswell as being convex between sidewalls 22 and 24. Top surface 26 andbottom surface 28 may also be formed to each include pyramidalconfigurations 26 a and 28 a, or other surface features, such assaw-teeth and serrations, to provide resistance against expulsion ofspinal implant 12 once inserted into the intradiscal space.

In the particular arrangement of spinal implant 12, a pair of fusionapertures 30 and 32 is formed through the top surface 26 and bottomsurface 28, apertures 30 and 32 being separated an intermediate wall 34,wall 34 being generally parallel to front wall 18 and rear wall 20. In aparticular arrangement, intermediate wall 34 is located approximatelymidway between said leading surface 18 a and said trailing surface 20 aof spinal implant 12. It should be appreciated however, that spinalimplant 12 may also be formed to have a single fusion aperture or morethan two apertures separated by one or more intermediate walls 34. Frontfusion apertures 30 and rear fusion aperture 32 are provided to befilled with appropriate bone growth promotion material to enhance fusionbetween opposing vertebral bodies. Intermediate wall 34 has an opening36 extending therethrough in communication with apertures 30 and 32 toallow bone growth promotion material to flow therethrough and to furtherserve in the positioning of spinal implant 12 during insertion, as willbe described. Sidewalls 22 and 24 may also be formed to have windows 38extending therethrough in communication with respective apertures 30 and32 for further flow of bone growth promotion material into and throughspinal implant 12. Windows 38 further provide assistance in thevisualization of the positioning of spinal implant 12 during insertion.Rear wall 20 is further formed to have an opening 40 extendingtherethrough, opening 40 communicating with rear aperture 32. Opening 40is formed to have internal threads 40 a for threaded engagement with rod16, as will be described. Rear wall 20 is further provided with a pairof laterally extending slots 42 extending into proximal trailing surface20 a for engagement with protrusions on the distal end of the inserter14 for stabilizing the spinal implant 12 against rotation duringinsertion, as will be set forth.

In the particular parallelepiped configuration being described, spinalimplant 12 has an overall maximum length L, a height H and a width W, asdepicted in FIGS. 2-3. The maximum length L is defined by the distancebetween distal leading surface 18 a and proximal trailing surface 20 a.The height H is defined by the maximum distance between the apices is ofthe top surface 26 and bottom surface 28. The width W is defined by themaximum distance between the exterior surfaces 22 a and 24 a ofsidewalls 22 and 24, respectively. For use as an interbody fusionimplant inserted from the lateral aspect, spinal implant 12 has in aparticular arrangement, a maximum length L of 50 mm, a height H of 8 mm,and a width W of 18 mm. However, for use as an interbody fusion implantfrom the lateral aspect, spinal implant 12 may have a maximum length Lranging from 40 mm to 60 mm, a height H ranging from 6 mm to 16 nm, anda width W ranging from 14 mm to 26 mm. It should be appreciated however,that when spinal implant 12 is used in interbody fusion applicationsinserted from other than the lateral aspect, such as with an anterior,posterior, posterior lateral or extrapedicular approach, the spinalimplant 12 may be formed to have dimensions suitable for suchapplications.

In the particular arrangement described, spinal implant 12 is formed ofpolyetheretherketone polymer (PEEK) for its strength and otherbiocompatible properties. Other suitable biocompatible materials may beused for spinal implant 12, including but not limited to,polyetherketoneketone (PEKK) and other polymeric materials. However,such materials are typically radiolucent and difficult to visualizeunder imaging techniques, such X-rays or fluoroscopy.

Referring again to FIG. 1 as well as to FIG. 5, details of the inserter14 are described. Inserter 14 comprises an elongate hollow barrel 44having a distal end 44 a and a proximal end 44 b. A lumen 44 c extendsfully centrally through barrel 44, lumen 44 c being configured and sizedfor receipt of elongate connection rod 16 therethrough. A handle 46 issuitably attached to the proximal end 44 b of barrel 44. The distal end44 a defines a contact surface 48 for contacting proximal (railingsurface 20 a of spinal implant 12 when inserter 14 is releasablyattached to spinal implant 12. A pair of laterally spaced protrusions50, in the form, for example, of pins having bullet shaped noses projectaxially from contact surface 48, protrusions 50) being configured andsized to be received into slots 42 of trailing surface 20 a of spinalimplant 12 during attachment of inserter 14 thereto. At the proximal end44 b of barrel 44 a threaded internal opening 52 is provided forthreaded releasable attachment to elongate rod 16, as will be described.Barrel 44 may be formed of a suitable metal, such as stainless steel, orother suitably rigid material.

Elongate connection rod 16 has a distal end 16 a and a proximal end 16b. Proximal end 16 b is externally threaded for an axial extent 54,threaded extent 54 providing a connector that is configured forreleasable threaded engagement into threaded internal opening 52 ofbarrel 44. A knob 56 is provided at the distalmost end 16 b of elongaterod 16, knob 56 being suitable for handling rod 16 during connection ofinserter 14 to spinal implant 12. Distal end 16 a is externally threadedfor an axial portion 58, threaded portion 58 providing a connector thatis configured for releasable threaded engagement into threaded opening40 a in the rear wall 20 of spinal implant 12.

As illustrated in FIG. 5, the distal end 16 a of elongate rod 16comprises a positioning element 60 projecting for an extent axiallydistally of threaded portion 58. Positioning element 60 and in aparticular arrangement is generally cylindrical having a length L_(P)and a diameter D. It should be appreciated that other configurations ofpositioning element 60 may be provided, such as but not limited to,square, rectangular or tapering configurations. Positioning element 60has at its distalmost end a substantially flat end surface 60 a, whichas will be described serves as a marker for assisting in the positioningof implant 12 into the intradiscal space. The axial dimension of lengthL_(P) is provided such that end surface 60 a lies within the spinalimplant 12 between leading surface 18 a and trailing surface 20 a at apredetermined distance from contact surface 48 of barrel 44. In theparticular arrangement being described, the diameter D of positioningelement 60 is configured to be received within opening 36 ofintermediate wall 34 and length L_(P) is formed such that end surface 60a resides approximately midway into opening 36 of intermediate wall 34.As such, end surface 60 a in this arrangement would establish theapproximate axial midpoint between leading surface 18 a and trailingsurface 20 a of spinal implant 12. It should be appreciated however,that the pre-determined distance surface 60 a extends from the contactsurface 48 of barrel 44 may be other than the axial midpoint of spinalimplant 12.

In accordance with the subject matter of the invention, the positioningelement is formed of a material more radiopaque than the material ofspinal implant 12. In a particular arrangement, positioning element 60is formed of stainless steel, although other suitable radiopaquematerials may be provided. In one particular embodiment, the entireelongated rod 16, including the positioning element 60 is formedintegrally as a one-piece rod of stainless steel.

Under suitable imaging techniques, such as with fluoroscopy or X-rays,the contrast between the radiopaque positioning element 60 and theradiolucent spinal implant 12 maybe readily observed, as shown in FIG.6. End surface 60 a of positioning element 60 serves as a radiopaquemarker clearly denoting in this particular arrangement the axial centerpoint of spinal implant 12 between leading surface 18 a and trailingsurface 20 a.

While the radiopaque marker described herein is particularly defined bysubstantially flat end surface 60 a with the positioning element beingformed of radiopaque material, it should be appreciated that aradiopaque marker may be provided in a different manner within thecontext of the subject invention. For example, the radiopaque marker maybe provided by a relatively sharp tip or apex of a curved surface at thedistalmost end of the positioning element 60. The radiopaque marker mayalso be provided by a hole through the positioning element 64 or astripe of material less radiopaque than the material of positioningelement 60. Further, positioning element 60 may be formed of radiolucentmaterial with a bead, coating or other deposit of radiopaque materialthereon. In each instance, the radiopaque marker would be located onpositioning element 60 such that when inserter 14 is attached to spinalelement 12 the radiopaque marker is located within spinal implant 12 atthe predetermined distance from contact surface 48 of barrel 44.

The preparation for inserting spinal implant 12 from the lateralapproach including the establishment of a surgical corridor through thetissue to the spine is more particularly described in commonly ownedU.S. patent application Ser. No. 14/342,563, entitled “Lateral ApproachExpandable Spinal Implant and Method”, filed on Mar. 4, 2014 by PeterBarreiro and published internationally as WO 2013/036707, the entirecontents of which are incorporated herein by reference. Having completedthe proper preparation and access for the lateral approach, the methodof locating the position of spinal implant 12 from the lateral approachis now described.

A kit of parts may be provided to the surgeon comprising inserter 14, aset of different size spinal implants 12 at least having differentlengths L, and a set of elongate rods 16 at least having differentpositioning element lengths L_(P). The rods 16 may be correlated withthe spinal implants 12 so as to match their respective lengths, suchcorrelation being provided by color coding or other suitable matchingindicia. Upon selection of a spinal implant 60 having a desired length Lfor the particular surgery and a rod 16 having a positioning element 60suitable for determining the axial midpoint of spinal implant 12,inserter 14 may be attached to the chosen spinal implant 12 by thechosen rod 16.

Referring again to FIG. 1, the selected rod 16 is inserted through lumen44 c of barrel 44 so that threaded extent 54 at the proximal end 16 b ofrod 16 threadably engages the threaded opening 52 at the proximal and 44b of barrel 44. As such, rod 16 is releasably attached to barrel 44. Atthis stage, the distal end 16 a, including threaded portion 58 andpositioning element 60 project distally outwardly of contact surface 48of barrel 44. Positioning element 60 is introduced into opening 40 athrough the rear wall 20 of spinal implant 12 until the threads ofthreaded portion 58 threadably engage the threads of threaded opening 40a. The surgeon continues to thread the threaded portion 58 into thespinal implant using knob 56 until the back distal surface 56 a of knob56 contacts the proximal end surface 44 d of barrel 44, as illustratedin FIG. 1. Once fully tightened, barrel 44 is compressed between backdistal surface 56 a of knob 56 and trailing surface 20 a of spinalimplant 12. During such assembly, barrel protrusions 50 engage withslots 42 in trailing surface 20 a for stabilizing the spinal implant 12against rotation during insertion. At this stage as illustrated in FIG.5, barrel 44, rod 16 and spinal implant 12 are fully assembled with endsurface 60 a being disposed within intermediate wall 34, therebyestablishing the axial mid-point of spinal implant 12 between leadingsurface 18 a and trailing surface 20 a.

The implant 12 is then introduced into the prepared intradiscal spacebetween two vertebral bodies 62 and 64 as shown in FIG. 7. Usingfluoroscopy, certain anatomical features of the spine such as thespinous processes 66 are discernible due to their bony characteristics.The progress of the insertion of spinal implant 12 may be monitoredunder fluoroscopy until the end surface 60 a of positioning element 60is substantially aligned with the anatomical center of spinous processes66 in the cephalad-caudad direction. As such, the axial midpoint ofspinal implant 12 is properly centered in the intradiscal space relativeto the sagittal plane of the patient by reference to the spinousprocesses. Once proper positioning is achieved, the surgeon may removethe inserter 14 by unthreading rod 16 from spinal implant 12, separatingrod 16 and barrel 44 from spinal implant 12, and leaving spinal implant12 properly positioned in the intradiscal space. It should beappreciated that while using the spinous processes 68 is suitable forcentering spinal implant 12 in the intradiscal space from the lateralaspect, other anatomical features, such as the dense cortical rims, beused for locating the position of a spinal implant, in particular, whereinsertion is an approach other than the lateral aspect.

Having described the particular arrangement of the apparatus 10 andmethod for locating the position of spinal fusion implant 12 in apatient during surgery, it should be appreciated that variations may bemade thereto without deviating from the contemplated scope of theinvention. For example, while the spinal implant 12 can be positionedinto the intradiscal space such that the axial midpoint of spinalimplant 12 is centered relative to the sagittal plane without the needfor radiopaque elements within spinal implant 12, additional featuresmay be desirable to determine different positions or orientations duringinsertion. As such, spinal implant 112, which may be otherwise identicalto spinal implant 12, may be provided with one or more radiopaquemarkers 114, as depicted in FIG. 8. Markers 114 may be permanentlycontained, for example, within the corners of spinal implant 112, eachmarker 114 being configured in the form of a pin or post having a lengththat extends downwardly into spinal implant 112. With such pins 114, andfrom the fluoroscopic view of FIG. 7, the surgeon would be able todetermine whether spinal implant 112 has rotated within the plane of theintradiscal space such that the axial centerline of spinal implant 114is not generally perpendicular to the sagittal plane as desired.Suitable corrections may then be made.

In another variation, positioning element 60, instead of being formedintegrally as a one piece unit with elongate connection rod 16, may beformed as a separate piece suitably attachable to the distal end 16 a ofelongate rod 16, as illustrated in FIG. 9. The proximal end 60 b ofpositioning element 60 may have an external thread for receipt into aninternally threaded opening 16 c extending into the distal end 16 a ofrod 16. It should be appreciated that other suitable joining structure,such as a press fit, may also be used to separably attach positioningelement 60 to rod 16. A set of separate positioning elements 60 may beprovided to the surgeon in the kit of parts, with each positioningelement 60 having a different length L_(P) that is correlatedrespectively to a length of the different spinal implants 12 in the kit.Each of the positioning elements 60 may be entirely formed of radiopaquematerial, such as stainless steel. In this arrangement, only a singleelongate connection rod 16 would be necessary. Accordingly, thearrangements described herein are intended to be illustrative and notlimiting.

What is claimed is:
 1. A method of locating a position of a spinalimplant during surgery for interbody fusion with reference to a featureof spinal anatomy, comprising steps of: providing a spinal implantformed of radiolucent material having a distal leading surface and aproximal trailing surface, said spinal implant having two fusionapertures therethrough divided by an intermediate wall, saidintermediate wall having therethrough an opening communicating with eachof said apertures; releasably attaching to said spinal implant aninserter having a positioning element projecting distally therefromalong an axis, said positioning element defining a radiopaque marker,said radiopaque marker being positioned interiorly of said spinalimplant within the opening of said intermediate wall, said marker beingdisposed so as to define a line of demarcation within the opening ofsaid intermediate wall and discernible in a view transverse to said axisand configured for identification of an axial point between said leadingsurface and said trailing surface; introducing said spinal implant bysaid inserter into an intradiscal space between two opposing vertebralbodies; using an imaging technique and with reference to a feature ofthe spinal anatomy, inserting said spinal implant into said intradiscalspace until said radiopaque marker is positioned in said intradiscalspace relative to said feature of spinal anatomy; and removing saidinserter with said radiopaque marker thereon from said spinal implantand leaving said spinal implant in said intradiscal space.
 2. The methodof claim 1, wherein said spinal implant is inserted from a lateralapproach and the spinal anatomical reference is to spinous processes,and wherein said spinal implant is inserted into said intradiscal spaceuntil said radiopaque marker is positioned generally in alignment withsaid spinous processes in a cephalad-caudad direction.
 3. The method ofclaim 2, wherein said intermediate wall is approximately midway betweensaid leading surface and said trailing surface.
 4. The method of claim3, wherein said marker is defined by a distal-most surface of saidpositioning element and wherein said positioning element is formed ofradiopaque material, said distal-most surface being discernible withsaid imaging technique in relation to said spinous processes.